The present invention relates to new polyether quinoxalines, which may be used in aerospace, automotive, microelectronic, optical, membrane applications such as gas separation membranes and molecular separation membranes.
Polyquinoxalines are a well established class of high performance thermoplastics with proven potential in aerospace, microelectronic and membrane applications.
Previous types of polyquinoxalines and polyphenylquinoxalines are normally prepared by the reaction of bis-alpha-carbonyl compounds with an organic tetramine, but other synthesis methods are also known.
Methods of synthesis of polyquinoxalines include the condensation of 1,4-diglyoxalylbenzene dehydrate with 3,3′-diaminobenzidine. The preparation of polyphenylquinoxalines by the reaction of combinations of two tetraamines, 3,3′-diaminobenzidine and 3,3′,4,4′-tetraminodiphenyl ether, with two bisbenzils, 4,4′-dibenzil and 4,4′-oxydibenzil is also known.
The formation of certain moldable polyetherquinoxalines from a wide variety of bis-alpha-carbonyl compounds and aromatic organic tetramines has been described, as has been the formation of polyphenylquinoxalines containing alkylenedioxy groups. These polymers have relatively lower glass transition and melt viscosity than other previously reported polyquinoxalines. As a result, they have better melt processability than the previously reported polyquinoxalines. But they still require the synthesis of tetramines and tetraketones.
A common organic tetramine, 3,3′-diaminobenzidine is commercially available but expensive and toxic. Aromatic tetraketones are not commercially available and require successive chemical steps to prepare, further increasing cost of the polyquinoxalines.
The preparation of polyquinoxaline by self condensation of a monomer having both a 1,2-diketone and a 1,2-primary diamine in the molecule has been described. Preparation of this monomer, 3,4-diaminobenzil, requires successive chemical steps and relatively expensive starting materials such as phenyl acetylene and palladium acetate.
Generally, polymerizations by aromatic nucleophilic substitution reaction to synthesize a polyarylether, where formation of the ether linkage is the polymer forming reaction, are well known in the art. Many commercially available melt-processable polyarylethers, such as polysulfones, polyetheretherketones or polyetherimides are prepared under aromatic nucleophilic substitution conditions in a polar aprotic solvent. Optimally, solvents used should be able to dissolve monomers, growing chains, and the final polymer at the polymerization temperature. Polar aprotic solvents such as dimethylsulfoxide, dimethylacetamide, dimethylformamide, n-methylpyrrolidinone, sulfolane and diphenylsulfone are generally used. A polymerization solvent should optimally be substantially free of water and the reaction is run under an inert gas atmosphere, such as nitrogen or argon. This polymerization can be performed using a single step process or a two step process, or using a heterogeneous two step process using a phase transfer catalyst.
In the single step process, a bisphenol and activated dihalide or dinitro monomer are polymerized in a polar aprotic solvent using an alkali metal salt, preferably potassium carbonate or sodium carbonate. In the single step process, potassium carbonate reacts with the phenol groups and forms reactive phenoxide salt and potassium bicarbonate. Over the range of 100-200° C., 2 moles of potassium bicarbonate decompose into 1 mole of carbon dioxide, 1 mole of potassium carbonate and 1 mole of water.
In the two step process, bisphenol is converted to a double alkali metal salt first, and then reacted with about stoichiometric quantities of activated dihalide or dinitro monomer. Polyarylethers can also be synthesized by a heterogeneous aromatic nucleophilic substitution reaction in relatively non-polar solvents such as o-dichlorobenzene, using a phase transfer catalyst having sufficient thermal stability under the polymerization conditions.
The preparation of other polyphenylquinoxalines by reacting bis-hydroxyphenylquinoxalines with activated difluoro monomers under aromatic nucleophilic substitution reaction conditions has also been disclosed. Preparation of bis(hydroxyphenylquinoxalines) requires successive chemicals steps and the activated difluoro monomers are expensive.
The formation of certain polyphenylquinoxalines by reacting bis-fluoro-poly-phenylated-quinoxalines with various bis-hydroxylated aromatic compounds under aromatic nucleophilic substitution reaction conditions is also known. The synthetic routes described eliminate the need for tetramines but still require expensive fluorinated starting materials as well as relatively high number of steps to synthesize the monomers.
Other polyether quinoxalines may be synthesized from a self-polymerizable mixture of monomers by a route that eliminates the need for the synthesis of tetraketones. However, that method still requires the use of expensive 4-fluoro-1,2-phenylenediamine and a high number of chemical steps.
Thus, it appears highly desirable to manufacture melt-processable polyetherquinoxalines from low cost starting materials.